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Entrapment and delivery of α-tocopherol by a self-assembled, alginate-conjugated prodrug nanostructure

Ye, Fayin, Astete, Carlos E., Sabliov, Cristina M.
Food hydrocolloids 2017 v.72 pp. 62-72
alpha-tocopherol, antioxidant activity, dispersions, emulsions, esterases, esterification, fluorescence emission spectroscopy, hydrocolloids, hydrolysis, lipid peroxidation, lipids, micelles, nanomaterials, nuclear magnetic resonance spectroscopy, oils, oxidation, pH, particle size, phosphates, polysorbates, solubilization, thiobarbituric acid-reactive substances, zeta potential
The aim of the study was to deliver α-tocopherol by a combination of prodrug and entrapment techniques, and to evaluate the ability of entrapped α-tocopherol to inhibit lipid oxidation in an oil-in-water emulsion. The amphiphilic alginate-α-tocopherol conjugate was synthesized via esterification reaction and confirmed by IR, 1H NMR, and fluorescence spectroscopy as well as esterase hydrolysis. The bound α-tocopherol in the conjugate was 20.6 μmol/g. The conjugate self-assembled into nanostructures in water, with a critical association concentration of 0.076 g/L. The percent entrapment and loading efficiency of α-tocopherol in the self-assembled nanostructures of the conjugate were, respectively, 4.92–16.82% and 78.83–92.32%, depending on the initial loading of α-tocopherol. Both blank and α-tocopherol-loaded nanostructures presented a negative zeta potential ranging from −50 to −65 mV and exhibited spherical shape with particle sizes in the range of 190–253 nm. More than 40% of α-tocopherol was retained after 216 h (i.e. 9 days) in phosphate buffer solutions (pH 7.4). The release of α-tocopherol was faster for nanostructures with lower α-tocopherol theoretical loading. Based on the thiobarbituric acid reactive substances assay for lipid oxidation, the blank nanostructures of the conjugate did not show antioxidant activity while the α-tocopherol-loaded nanostructures protected lipids against oxidation better than free α-tocopherol entrapped in the oil phase or in Tween 20 micelles. The results indicated that the newly prepared α-tocopherol-loaded nanostructure is a promising platform for solubilizing and delivering antioxidant activity of α-tocopherol in aqueous dispersions.